1. Field of the Invention
Automobiles manufactured within the last several years have incorporated successive improvements to provide greater operational safety for their occupants and to significantly reduce the production of atmospheric-polluting compounds in engine exhaust gas emissions. There have also been improvements in handling, overall performance, and comfort afforded occupants of recent model automobiles.
However, these positive improvements have generally been accompanied by a degradation of the fuel consumption efficiency in these late model automobiles. Furthermore, this increase in fuel consumption is at least in part related to the positive improvements noted above. In particular, increased fuel consumption may be related to three general causes. First, equipment designed to augment vehicular safety and ease of operation such as power brakes and power steering require the use of engine power which is necessarily subtracted from the power available to propel the automobile. Second, equipment designed to augment vehicular comfort and convenience such as automatic transmission, air conditioning, and, to a lesser extent, power operated windows and other accessories, similarly require engine power necessarily subtracted from propulsive power. Third, engineering and design modifications introduced to reduce engine exhaust pollutant emissions reduce fuel consumption efficiency for the following reasons. The engine compression ratio has been reduced, changes have been made in valve and ignition timing and, in some cases, an auxiliary air injection pump for supplementing complete combustion of exhaust gases is used, and this pump imposes loading upon the engine.
On a typical vehicle having contemporary emission control equipment, automatic transmission, air conditioning and other power accessories, a widely utilized carburetor control system employs two separate and distinct idle speed fixed throttle settings for the engine. The primary or curb operating engine idle speed with automatic transmission engaged is approximately 630 rpm. With the automatic transmission in neutral, the engine idle speed will increase to approximately 860 rpm. This 860 rpm speed is significantly greater than the "no load" minimum of about 500 to 550 rpm required by the same engine (when properly tuned) to run smoothly if used in an automobile having manual transmission and no power accessories.
The fully equipped automobile must conventionally idle at the higher rate of 630 rpm with automatic transmission engaged for the following reasons: At this idle speed, the engine produces enough power to overcome the inherent load of the automatic transmission when the vehicle is stationary with such transmission engaged; plus, enough power to drive any or all other power accessories which may be turned on. At standstill, the incremental increase in load caused by the actuation of each accessory causes an incremental decrease in engine speed so that the idle speed with all possible accessories operating may be reduced to approximately 550 rpm.
The secondary or shut down fixed throttle setting equivalent to approximately 400 to 500 rpm is used to stop the engine. The lean fuel-air mixture and high engine temperatures brought about by emission control equipment frequently cause the engine to run by auto-ignition or "dieseling" after the ignition is switched off. This undesirable tendency to "diesel" after being switched off is also made worse by the more open idle throttle setting required to provide enough power to drive the automatic transmission and other power accessories. The more open throttle admits a more dense fuel-air charge to the cylinders and hence higher compression and cylinder temperatures are developed during idling. In some recently manufactured automobiles, idle speeds have been increased to reduce the pollutants in exhaust emissions. This practice further aggravates the problem of "dieseling". It is also wasteful of fuel. However, when the throttle control arm is at this secondary setting, the engine will reliably stop.
The secondary idle speed is controlled on typical contemporary engines by a mechanical stop screw adjustment. The primary idle speed is controlled by a solenoid operated idle stop. This solenoid idle stop is activated when the ignition is switched on.
In summary, added power accessories require that automotive engines idle at no load at a relatively high idle speed which decreases with all accessories operating to a minimum reliable idle speed of approximately 550 rpm. This requirement of idling significantly faster in the no-load condition results in increased fuel comsumption.
During deceleration of the vehicle or when driving downhill and the throttle control arm rests at its stop in the closed position, while the transmission is engaged so that vehicle momentum is effectively driving the engine through the transmission to produce engine speeds greater than that value of the substantially constant controlled idle speed, the apparatus of this invention causes the throttle to close as far as its most closed secondary setting regardless of how many power operated accessories are being operated, thereby conserving fuel and producing more effective engine braking action.
The present invention is intended to reduce fuel consumption resulting from the prior art fixed idle speed throttle opening by providing a simple apparatus easily retrofittable to existing engines and also adapted for original installation on new engines. This improved fuel consumption is achieved by causing the engine to idle at a substantially constant minimum speed consistent with smooth engine operation regardless of the amount of non-propulsive accessory load which the engine must drive and by controlling throttle opening when the throttle control arm rests on its stop in the closed position during operation when the vehicle is driving the engine. The invention permits the engine at each instant of time to operate at varying amounts of power, delivering less at idle (than in the prior art) when the engine is driving and absorbing more (than in the prior art) when the engine is being driven with the driver's foot removed from the accelerator pedal under the conditions of stop and go city driving and during highway driving in hilly terrain.
During steady state open throttle driving, such as on a level highway, the apparatus embodying this invention has no effect upon engine operation nor fuel consumption.
2. Description of The Prior Art
Devices are presently known for minimizing variation in idle speed of vehicular internal combustion engines. Such a device is disclosed in U.S. Pat. No. 3,577,962 -- Ojala (assigned to Ford Motor Company) employing a centrifugal or magnetic unit to control the application of intake manifold pressure (suction) to a vacuum actuator which in turn drives a V-shaped cam. This system acts to open the throttle blade slightly during engine deceleration to improve exhaust emissions.
Other devices which control throttle position include U.S. Pat. Nos. 3,287,007 -- Schoeppach; 3,682,148 -- Harrison et al.; 3,730,153 -- Harrison et al.; 3,254,638 -- Walker et al.; 2,929,266 -- Baker et al.; 2,782,025 -- Olson; and 2,913,921 -- Gordon.
The devices described in the patents set forth above have certain deficiencies. Some are relatively complex and hence expensive to manufacture and maintain. Typically, they may not be easily fitted to existing engines and consequently should be installed as original equipment at the time of engine manufacture. The device shown in the Ojala patent opens the throttle blade slightly during engine deceleration, when the V-shaped cam moves beyond the normal idle position, which is opposite to the manner of operation of the apparatus described herein. None of the above is shown to function in mechanical conjunction with the antidieseling solenoid, which is in current wide use to provide reliable stopping of the engine.